Nutrient and popping characteristics of Wyoming‐grown Peruvian popping beans

Abstract American consumers fall short of dietary fiber intake recommended by dietary guidelines. Beans provide protein and fiber, however, less than 14% of adults include them in their daily diets. Nuña beans (Phaseolus vulgaris L.), a class of common beans originated in South America and cultivated for growth in North America, possess a unique set of characteristics including flavor profile, popping ability, and nutrient content that may appeal to consumers. The purpose of this study was to evaluate a unique line of Wyoming‐grown popping beans to (1) determine nutrient characteristics and (2) assess popping percentage and shelf stability. Crude protein content was determined for five lines grown in Wyoming utilizing the Dumas method for nitrogen quantification. Total fatty acid content and a fatty acid profile for one line (CO49957) was determined by gas–liquid chromatography. Popping percentage was assessed by heating beans in canola oil in a cast iron pan to induce popping. Storage duration impact on popping was evaluated on CO49957 at 6, 12, and 15 months after harvest. Crude protein content was significantly different between all five lines. Total fatty acid content of CO49957 averaged 2.90 g/100 g wet weight. Average fatty acid profile of CO49957 popped in canola oil comprised oleic acid (41.4%), linoleic acid (20.4%), α‐linolenic acid (18.6%), palmitic acid (10.4%), and stearic acid (2.23%). Popping percentage was 90% (baseline), 100% (6 months), 87% (12 months), and 80% (15 months). Popping beans provide plant‐based protein and fiber while maintaining adequate levels of popping percentage with prolonged storage.

. Beans were air dried, hand shelled, and stored in paper bags. Popping beans used exclusively for crude fatty acid analysis (CO49956, PI577678, WI19, WI21) were grown in UW greenhouses in 3 gallon pots containing a mixture of soil, pine bark mix, and sand (1: 1:1, v,v,v). Planting date was October 12, 2018. Seeds from CO49956, WI19, and WI21 were harvested 74 days after planting.
Seeds from PI577678, a photoperiod sensitive line, were harvested 135 days after planting. Seed shelling and storage followed the procedure described for CO49957.

| Popping percentage/shelf stability
Initial testing in the HNF Lab at the UW included heating beans for 1 to 4 min to induce popping using a microwave and air popper (no fat source) and aluminum pan on electric stove and cast iron pan on commercial gas range (using canola oil). Initial testing produced inconsistent popping and quality of beans using the microwave and aluminum pan. Thus, pilot popping testing was conducted on CO49957 using three heating methods to determine finalized method of popping: (1) cast iron skillet on a gas range using canola oil, (2) cast iron skillet on gas range using lard, and (3) air popper.
Beans popped with a fat source were heated in a cast iron skillet F I G U R E 1 Beans popped in the Human Nutrition and Food laboratory at the University of Wyoming from the CO49957 line. with one teaspoon (5 ml) of canola oil or lard to induce popping.

Beans popped in the air popper (Presto Poplite Hot Air Popcorn
Popper) were added to heating chamber for a period of 0.75 to 1.5 min to induce popping. Popping percentages for each method during the pilot testing did not significantly differ. Therefore, the method using canola oil and a cast iron skillet was chosen for the current study as this method was thought to be more representative of oil use in the United States and energy efficient preparation used traditionally with nuña beans. Popping beans (CO49957) were popped in the HNF laboratory. Beans (n = 10, N = 30) were heated in one teaspoon (5 ml) of canola oil in a cast iron skillet until the oil reached a temperature of 250°C for a period of 1.5 to 2.0 min to induce popping. Temperature was measured using an infrared thermometer (ELECALL EIRT550E) held 12 inches above the surface of the skillet. Popping percentage of line CO49957, from the 2019 harvest, was assessed at baseline (0 months), 6 months, 12 months, and 15 months of storage. Popping percentage was calculated as (popped beans/total beans assessed) × 100.

| Fatty acid analysis
Beans popped in canola oil followed the procedure outlined earlier.
Excess oil was manually removed with a paper towel from beans popped in oil, and beans were ground to a fine powder using a food processor. Beans popped in the air popper followed the procedure outlined earlier. Air popped beans were then placed directly into the food processor and ground into a fine powder. Samples were partitioned into 0.5 g sample freezer bags, treated with nitrogen gas, sealed, and stored at −80°C until fatty acid analysis.
Fatty acid analysis was conducted by gas-liquid chromatography (GLC) and fatty acid methyl esters were prepared according to the method described by Weston et al. (2008). Briefly, triplicate 0.5 g samples of popping bean were weighed into 16 × 125 mm screw-top tubes containing 0.5 mg of tridecanoic acid as an internal standard.

| Crude protein percentage
Crude protein analysis was performed by the WY State Analytical Lab. A LECO TruMacN was used to achieve combustion via the Dumas method for the quantitative determination of nitrogen. The samples (CO49957, CO49956, PI577678, WI19, WI21) were combusted in a furnace composed of "pure" oxygen, at 1100°C, to ensure complete oxidation. The combustion gas was then carried through a series of reagents to remove moisture and carbon dioxide. This allowed for the conversion of nitrogen oxides to molecular nitrogen. These reagents ensured that the sample reaching the detector was nitrogen.
The nitrogen was then quantitated using a thermal conductivity (TC) detector. The quantitated nitrogen was then converted to percent crude protein by using the protein conversion factor of 6.25.

| Statistical analysis
Analysis of popping percentage compared the difference of baseline (0 months) popping and repeated testing of a time period of 6, 12, and 15 months using repeated measures ANOVA. Analysis of crude protein percentage compared the difference of lines CO49957, CO49956, WI19, WI21, and PI787678 using one-way ANOVA. Mean value for each line was compared after analysis was repeated in triplicate. Post hoc Tukey's correction was performed to account for family-wise error. Total fat content and fatty acid composition are reported as the mean value for each nutrient after analysis was repeated in triplicate. Analysis of total fat content and fatty acid profile was accomplished using two-way ANOVA. Alpha Type I error rate was set at 0.05 for statistical significance. Statistical analyses were performed using Minitab version 18.0 and IBM SPSS version 26.

| Fatty acid profile
No significant difference was found when comparing the fatty acid profile of CO49957 harvest year 2018 and 2019 from either airpopped or oil-popped beans. Therefore, harvest years were averaged and expressed as either air-popped or oil-popped in Tables 2   and 3.
Crude protein differed significantly (p < .001) between all lines.

| DISCUSS ION
Popping percentage was not significantly reduced at any time point as compared to immediately postharvest. An increase in popping percentage was observed at 6 months (100%) as compared to immediately postharvest (90%). Although seed moisture was not determined in this study, the increase in popping percentage could be explained by a decrease in moisture content as the beans aged. Vorwald and Nienhuis (2009) showed that nuña beans with a seed moisture content below 5% maximized popping percentage. A numeric decrease in popping percentage was observed at 12 and 15 months, but was not significant. Other researchers identified popping percentage between 17% and 81% within 3 months of harvest, but were not evaluated for popping ability after 3 months (Pearson et al., 2012). Future research should extend the duration of shelf storage to determine if a significant decline in popping percentage is observed beyond 15 months of storage time. Onset of popping averaged 233°C (baseline), 228°C (6 months), 228°C (12 months), and 221°C (15 months). These results are slightly lower than those reported by Vorwald and Nienhuis (2009), who showed that ideal popping temperature was above 244°C. The difference in popping temperature could be explained by differences in popping modality. Vorwald and Nienhuis (2009) used an air popper that heats beans through convection. In this study, beans were heated through conduction. Popping trials in this study were conducted at an altitude of 7220 feet. Vorwald and Nienhuis (2009)  Increased cooking time requires collecting additional vegetation as fuel, and local vegetation is often a scarce commodity in the highlands of Peru (Zimmerer, 1992). While consumers in the highlands of Peru benefit from the popping bean's decreased fuel demand, consumers in the United States could benefit from decreased cooking time by using less propane, natural gas, or electricity for cooking.
The fatty acid profile and total fat content of popping beans were similar to the fatty acid profile of other common bean varieties  (Blondeau et al., 2015). α-Linolenic acid has been shown to have neuroprotective, anti-inflammatory, and antidepressant properties and is required for normal brain development and function (Blondeau et al., 2015). Although the total fat content of popping beans was relatively low, inclusion of popping beans in a healthy diet may contribute to the aforementioned health attributes.
Fatty acid profile detailed in Table 3  half cup serving of popping beans prepared in canola oil would contain 2.64 g of total fat. Crude fat content of air popped beans is much lower than crude fat content of air popped popcorn (3.9 g/100 g) as determined by Khan et al. (2016). As popcorn is a popular snack food with a significant commercial demand, low-fat microwavable options have been developed with a fat content as low as 5.5 g/100 g (Nguyen et al., 2012  TA B L E 4 Fatty acid composition (% of total profile) and total fat content of air popped popping bean, commercial black bean, and commercial kidney bean intake without concurrent saturated fat intake as would be seen with beef and full-fat dairy consumption. For example, dry kidney beans contain 0.15 g of saturated fat in 100 g, while whole milk contains 1.86 g/100 g and 80% lean ground beef contains 7.58 g/100 g (USDA Food Data Central). Dry bean consumption has been associated with a protective effect against the development of chronic diseases including a decreased incidence of diabetes, cardiovascular disease, and prostate, colon, and breast cancer (Mitchell et al., 2009). Crude protein content of the five popping bean lines examined in this study ranged from 17.3% to 22.1%. This is similar to the range of crude protein content of black beans (20%-25%) reported by Evangelho et al. (2017) and crude protein content of red kidney beans (23.9%) and pinto beans ( providing the stock seeds.

CO N FLI C T O F I NTE R E S T
The authors declare that they do not have any conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.

E TH I C S S TATEM ENT
This study does not involve any human or animal testing.